The present invention relates to key mechanisms for use in business machines such as typewriters, teletypewriters, calculators, adding machines, cash registers, etc. and equipment such as computer inputs, keyboard modules, and the like. More particularly it relates to key mechanism arrangements for use in keyboards to provide a snap action by a member corresponding to a selected key for initiating remote function.
Key mechanisms used in a keyboard of a modern business machine or equipment must be designed to satisfy increasing demands placed upon such machines. To achieve this, key mechanisms must be rapid in response and reliable in operation without sacrifice of economical manufacture to be widely acceptable. There is a need for versatile key mechanisms that are adaptable for a variety of keyboard usages; for example, in connection with machines operably controlled by either electronics or mechanical mechanisms. A most important design consideration for key mechanisms is its "touch" or "feel". A desirable approach is to provide a mechanism having a "tactile touch", that is to say, a key device operation that offers a certain resistance followed by a breakaway feeling usually caused by sudden removal of resistance felt by the operator. This provides the user with an effective pleasant sense of successful actuation of a selected key. Key mechanisms used in modular keyboards have many advantages including versatility in their use with many different types of machines without significant alterations in design. Additionally, should repair be required, a replacement keyboard may be employed thus minimizing machine shut-down time.
Key mechanism arrangements for keyboards as disclosed in the prior art include disadvantages. For example, U.S. Pat. No. 3,612,240 granted to R. L. Parker, discloses a key mechanism having pivoting keylevers with an element pivotally mounted and spring biased on one side of each keylever. A pin is fixed on each element and is cooperable with a deflector bar for controlling the actuation of the element upon depression of the keylever to a desired level. The element is then released and under the influence of the spring is caused to swing. The swing motion of the element is used to initiate remote devices corresponding to the selected keylever.
The Parker patent is an improved key mechanism, in that it is versatile in its use as shown and described in connection with the different disclosed embodiments. However, such versatility has a major disadvantage in that when applied to the different embodiments, a unique element is required. Moreover, for three of the disclosed embodiments the element must be differently constructed for use with each keylever, requiring an extensive costly part inventory for the manufacturer as well as complicating part replacement. The construction has another disadvantage in that the deflector bar which is critical for operation is elongated to effect all the elements and includes, for each element, teeth, each with an angular face and a cam notch construction. Such part complexities are difficult to produce requiring costly manufacturing processes as well as elaborate inspection techniques. Additionally, the deflector bar is subjected to frictional wear which after extended use may become inoperative requiring part replacement that is time consuming and difficult. Further, since this mechanism includes many frictional sliding part arrangements, lubrication is an important factor for reliability and quick response during operation. Such lubrication must be applied with skill, as too little is ineffective and too much attracts foreign particals such as dust and erasure droplets which may cause malfunction of the mechanism or require the addition of a costly insert cover. Further, the Parker patent does not disclose any mechanism for a desired key touch feature.
A prior art patent U.S. Pat. No. 403,288 issued to F. H. Richards, is an example of a simple mechanical movement initiated by key depression. This patent discloses a pivotal hammer for disengaging a hook upon depression of a key. The hammer is centrally pivoted having a rigid handle extending toward resting engagement with a stem of the key. The other end of the hammer is flexible about an abutment stop and has a hammer head at its end. A pair of springs are needed to restore the mechanism after actuation. Depression of the key causes the hammer to pivot, limited by the flexible end contacting the stop, however, momentum causes the hammer head to continue an amount sufficient to strike the hook. In this embodiment, as stated in the description, "the key should be forcibly struck" which is most unfavorable. The resulting movement of the fingers of the operator is suddenly stopped, thereby causing operator fatigue, and even possible injury to the finger tips. An improved second embodiment of the mechanical motion is disclosed wherein a detent is provided for momentarily preventing hammer movement until a spring has built up sufficient compression to overcome the detent.
The Richards patent has a disadvantage in construction due to several inherent part complexities. The hammer has a multitude of differently shaped sections, making such a part inconceivable to manufacture economically (at a high volume rate). Further, each key is closely contained in a housing for controlled vertical movement requiring costly manufacturing processes in obtaining satisfactory part relationship. The Richards patent does not provide a means for a desirable key touch, conversely, as mentioned, the mechanism is most cumbersome to use. For these reasons the mechanism of the Richards patent is not readily adaptable for the high volume requirements of modern manufacuters.